Selective Hydrogenation Of Benzene Over Ru-Zn/ZrO₂ Catalysts Prepared By Impregnation Method

Adipic acid and caprolactam is the raw material for preparing nylon-66 and nylon-6, the traditional catalytic oxidation of cyclohexane route has low per-pass yield, complex products, by-products can not be reused and other shortcomings, and the new selective hydrogenation of benzene to cyclohexene route has a green, energy-saving and safety advantages, which attracted much attention. However, the selective hydrogenation of benzene to cyclohexene is thermodynamically unfavorable, therefore, the special structure of catalysts prepared and catalyst systems for promoting cyclohexene generation from the dynamics strategies are the core of the study. In this paper, the impregnation method for preparation of Ru-Zn/ZrO₂ catalysts was studied in detail, the main work is as follows:Preparation of supported Ru-Zn/ZrO₂ Catalyst by a two-step impregnation method:we presented a two-step impregnation preparation method for supported Ru-Zn/ZrO₂ catalysts, the effect of different Zn contents on catalyst performance was studied. When Ru was 10.0 wt% and Zn was 2.78 wt%, the selectivity of cyclohexene （S50） reached 81.6%, slightly higher than the level of industrial catalysts, arid the specific activity （γ50） was greater than 800 g benzene/（gRu·h）, more than four times the industry catalysts, saving the amount of precious metals Ru. The Effect of the catalytic properties of alkali treatment after reduction was also studied, and it is found that alkali treatment after the reduction will help improve the catalyst selectivity to cyclohexene. The effect of catalyst reduction temperature was investigated and it is found that the catalyst reduced at 200 ℃ showed the best cyclohexene selectivity. Recycle stability of the catalyst was studied; when the amount of catalyst was 0.9 g, the catalyst showed good stability, indicating that it has a good industrial application value. Also effects of of catalysts preparation such as Ru content, Zn precursor, other additives on catalyst performance, and effects of reaction time, amount of catalyst, ZnSO4 added amount, stirring rate, reaction pressure, temperature on the catalytic properties were also studied.Effects of support structure on Ru-Zn/ZrO₂ Catalyst:ZrO₂ supports were prepared, then supported Ru-Zn/ZrO₂ catalysts were fabricated. The effect of the catalyst support structure on cyclohexene selectivity was studied and it is found that small secondary particle diameter of support, moderate specific surface area, the larger pore size, specific pore volume and degree of crystallinity will help improve the performance of the catalyst reaction.Mechanism investigation of selective hydrogenationof benzene over Ru-Zn catalysts:unsupported Ru-Zn catalysts were prepared by coprecipitation method from the homemade ZrO₂ supports with different structures, the morphology of basic zinc sulphate after reaction was observed by scanning electron microscopy; by comparison of the performance of the catalyst under different conditions, it is presented that Ru surface lattice defects will help improve the selectivity of cyclohexene, and that catalyst surface wrapped by basic zinc sulphate can hold water, making the stagnant water layer of the catalyst surface thicker, thereby increasing the selectivity of cyclohexene.